The invention relates to a belt tensioner for a vehicle occupant restraint system comprising a housing, a working chamber into which the compressed gas being released in the case of restraint is flowing, a pull rope extending through an opening within the housing and a sealing bush for sealing the working chamber against the opening between the pull rope and the housing.
Belt tensioners comprising a pull rope as tension transmission means are known. The high requirements made to the tightness between the pull rope and the housing to ensure reliable functioning in the case of restraint can only be achieved by covering the pull rope or by a sleeve system.
When directly sealing the pull rope by a soft sealing element it is hardly possible to bring assembly-optimized dimensions of the sealing element in line with the dimensions required for high requirements to tightness. On the other side, sealing elements having diameters required for proper sealing in the threading procedure can be mounted with considerable effort only.